Ultrasonic imaging device

ABSTRACT

An ultrasonic imaging apparatus of the present invention performs a tentative scanning of ultrasound to the inside of a living body with delay time corresponding to average sonic velocity, calculates delay time error in a delay time error detecting circuit, by using received signals from each channel to which delay control has been performed in a digital delay circuit, compares in a delay time comparing unit said calculated data with a plurality of delay time error data corresponding to various sonic velocities using sound velocity as the parameter stored beforehand in a sound velocity-derived delay time error storing unit, selects among those sonic velocities the one matching the delay time error data with a sonic velocity selecting unit, and calculates the sonic velocity within the living body. Then, said calculated sonic velocity is fed back to CPU, and the delay data on the delay applied in the ultrasonic scanning is provided to a delay circuit. In this manner, ultrasonic velocity propagating in a medium can be calculated with simple calculation, and the imaging can be done using the delay data corresponding with said velocity in the ultrasonic imaging apparatus.

FIELD OF THE INVENTION

[0001] The present invention relates to an ultrasonic imaging apparatusfor examining internal structure of a living body and goods, such as anultrasonic diagnosis apparatus used for medical diagnosis, and anon-destructive examination apparatus used for non-destructiveexamination of goods. More particularly, it relates to an ultrasonicimaging apparatus that can obtain images of high quality even when theinternal structure of a living body and goods are different in theirpropagation velocity of ultrasonic wave.

BACKGROUND OF THE INVENTION

[0002] In a linear scanning type ultrasonic imaging apparatus,ultrasound is received and transmitted by simultaneously driving theelements of an arrayed transducer group forming an aperture, which areselected by a aperture-selecting switch to form the aperture for aplurality of ultrasonic array transducers. Then, by shifting theaperture successively, the inside of the living body or goods islinear-scanned by an ultrasonic beam. Also, in a sector scanning typeultrasonic imaging apparatus, the inside of the living body or goods isscanned by inclining the ultrasonic beam, not shifting the aperture. Inboth the linear method and the sector method, a focus point is set up inthe living body or the goods, and then a driving pulse is provided toeach transducer in a delay-controlled manner so that all the ultrasonicwaves transmitted from ultrasonic transducer group in the aperture canarrive at the focus point simultaneously.

[0003] For performing the delay control, a transmission delay circuit isprovided. Output of the driving pulse generated from a transmittingcircuit is delayed, said driving pulse is supplied to each transducer inthe selected aperture through the transmission delay circuit, andultrasonic beam is transmitted.

[0004] Reflection echoes from the object are received by a plurality ofthe ultrasonic transducers in the receiving aperture selected, and saidreflection echoes are input to a receiving circuit connected to thisplurality of ultrasonic transducers through an transmitting/receivingseparation circuit. Said echoes are turned into signals having a goodamplified dynamic range, and then, said signals are converted intodigital signals by a plurality of analog digital converters. Thesesignals are time-converted so that all received echoes arrive at thesame time and then added up and output with a phase adjustment unit,which is comprised of a digital delay unit and an adder circuit. Thisoutput is used as receiving beam signals. Logarithm compression,filtering and γ correction are performed on this output by a signalprocessing unit, and the output is displayed after performing conversionof the data, such as coordinate transformation, or interpolation.

[0005] Delay data for delaying transmission and reception of signalsdescribed above is calculated by dividing the distance from eachtransducer to the focus point by propagation velocity of ultrasound inthe object, thus deriving a time value. But, the structure of the mediumto be examined is not uniform. Propagating velocity of ultrasound withina body is varied, depending for instance on whether the person is obeseor muscular. Thus, in the present circumstance, delay data is set up inthe apparatus by positing the average velocity of ultrasonic wavespropagating in the living body.

[0006] When the actual sonic velocity is exceedingly different fromposited velocity due to individual differences, a clear image cannot beobtained since ideal focusing is not performed.

[0007] As an example of method of estimating ultrasonic propagationvelocity in living tissue, Japanese Patent Laid-open Publication No.Heisei 6-269447 can be referred. In this method, various coefficients ofthe medium being studied, including sonic velocity, are hypothesized, ahypothetical model of the transformation of a propagating waveform iscalculated with a theoretical formula using those coefficients, bycomparing the calculated waveform with measured waveform improvedestimates of the above coefficients, including sonic velocity, areobtained.

[0008] As an example of an ultrasonic diagnostic apparatus performingoptimum focusing by correcting the sonic velocity, Japanese PatentLaid-open Publication No. Heisei 2-274235 can be referred. In theapparatus of said example, an operator sets the sonic velocity of themedium from the console and then modifies the focus. Also, as an exampleof an ultrasonic diagnostic apparatus that can perform focusingautomatically in a region where the focus is not made on a sectionalimage, Japanese Patent Laid-open Publication No. Heisei 8-317923 and No.Heisei 10-066694 can be referred. In the apparatus of this example, thehuman body is regarded as a non-uniform medium and the delay time iscontrolled in accordance with the living body, which is the object to beexamined. According to this method, optimum focusing can beautomatically obtained.

[0009] In the art disclosed in Japanese Patent Laid-open Publication No.Heisei 6-269447, however, the medium composition has to be hypothesizedand also the calculation method is complicated. Moreover, the long timeit takes to do this calculation and compare it with the actual measuredwaveform is a drawback. The art disclosed in Japanese Patent Laid-openPublication No. Heisei 2-274235 does not contain a method ofautomatically estimating sonic velocity, it puts a great burden on theuser, as well as lacking accuracy. Moreover, since the arts shown inJapanese Patent Laid-open Publication No. Heisei 8-317923 and No. Heisei10-066694 do not attempt the estimation of sonic velocity of the medium,good images cannot be obtained for the whole range of ultrasonic beamscanning object, which is a problem to be solved.

DISCLOSURE OF THE INVENTION

[0010] The first object of the present invention is to provide anultrasonic imaging apparatus that can calculate sonic velocity of themedium quickly and control delay time using this delay time.

[0011] The second object of the present invention is to provide anultrasonic imaging apparatus having better operationality, which canautomatically perform focusing with the sonic velocity suited to themedium, without an operator having to input this sonic velocity.

[0012] The third object of the present invention is to provide anultrasonic imaging apparatus that can perform focusing uniformly andmore sharply throughout the whole region which is subjected toultrasonic beam scanning; that is, throughout the whole image.

[0013] Finally, the fourth object of the present invention is to providean ultrasonic imaging apparatus that can provide the estimated sonicvelocity to the operator in visible form.

[0014] To achieve the above objects, the present invention comprises:

[0015] an ultrasonic probe having a plurality of built-in transducersfor transmitting ultrasound towards an object to be examined andreceiving the echoes from it;

[0016] means for converting each echo signal that is output from aplurality of transducers in said ultrasonic probe into digital signals;

[0017] phase adjustment means for adjusting phase of echo signals byapplying said predetermined delay time data to each digitized echosignal that is output from said digital signal transforming means;

[0018] means for calculating delay time data corresponding to ultrasonicpropagation velocity in the object, using the output signals from saidbeam adjustment means;

[0019] means for forming received beam signals by applying the delaytime data calculated by said delay time data calculating means to outputsignals from said phase adjustment means; and

[0020] means for displaying an image on a displaying means byimage-processing the received beam signals formed by said received beamsignal forming means.

[0021] And, said delay time data calculating means is characterized bycomprising:

[0022] means for calculating delay time errors of said echo signalsoutput from said beam phase adjustment means by comparison with echosignals from the respective transducers that contributes to reception ofsaid echo signals;

[0023] storing means for storing data of delay time errors correspondingrespectively to a plurality of ultrasonic propagation velocities; and

[0024] a sonic velocity selecting unit for selecting the ultrasonicpropagation velocity by comparing the output of said calculating meanswith the delay time data stored in said storing means.

[0025] Further, said delay time error data storing means ischaracterized in that delay time errors corresponding to a plurality ofultrasonic transducer channels are stored as a plurality of delay timedistributions, using sonic velocity as a parameter.

[0026] Further, said delay time error calculating means is characterizedin that delay time errors are calculated by using data in the depthdirection of a plurality of output signals of a certain region from saidphase adjustment means.

[0027] Further, said delay time error calculating means is characterizedin that delay time errors are calculated by using data for the wholeregion in the depth direction of a plurality of output data from saidphase adjustment means, as well as that this calculation is performedthroughout the predetermined ultrasonic scanning region that is formedby a plurality of the received beams.

[0028] Further, said ultrasonic imaging apparatus is characterized inthat sonic velocity storing means is provided for storing ultrasonicpropagation velocity corresponding to a plurality of delay timedistributions that are stored in said delay data storing means, and saidsonic velocity selecting unit calculates sonic velocity corresponding tothe selected delay time data by comparing with contents stored in saidsonic velocity data storing means.

[0029] Further, said ultrasonic imaging apparatus is characterized bycomprising means for displaying the sonic velocity data on the displayscreen of said displaying means, said sonic velocity data beingcalculated at said sonic velocity selecting unit.

[0030] Further, said ultrasonic imaging apparatus is characterized bycomprising means for setting ultrasound propagation velocity estimatedfrom the physical constitution of the object to be examined, and meansfor calculating errors of propagation velocity using the ultrasoundpropagation velocity that is set by said setting means, and theultrasonic propagation velocity in the object that is calculated fromoutput signals of said phase adjustment means, said received beam signalforming means produces received beam signals by adding propagationvelocity errors calculated by said calculating means, and ultrasonicpropagation velocity that is set at said setting means to output signalsof said phase adjustment means.

[0031] Further, said ultrasonic imaging apparatus is characterized bycomprising means for converting delay time errors calculated by usingdata of a plurality of output signals in all region in the depthdirection from said phase adjustment means into a sonic velocity datadistribution, and then displaying it as a sonic velocity distributionimage on the screen of said display means.

[0032] And further, said ultrasonic imaging apparatus is characterizedin that said sonic velocity distribution image is displayed with huesvarying in accordance with a difference of sonic velocity, that sonicvelocity distribution image is displayed together with and theultrasonic cross sectional image simultaneously on the display screen ofsaid display means, and said sonic velocity distribution imagesuperimposed on the ultrasound cross sectional image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a block diagram showing an embodiment of the structureof a delay time controlling unit in an ultrasonic imaging apparatus ofthe present invention.

[0034]FIG. 2 is a block diagram showing an embodiment of the structureof a delay time error-calculating unit of the present invention.

[0035]FIG. 3 is a block diagram showing the outline structure of theultrasonic imaging apparatus of the present invention.

[0036]FIG. 4 is a graph representation of contents of the sonicvelocity-derived delay time error relations storing unit.

[0037]FIG. 5 is a diagram to explain the embodiment of displaying sonicvelocity distribution.

BEST MODE FOR CARRYING OUT OF THE INVENTION

[0038] Hereinafter, an embodiment of the present invention is minutelydescribed using diagrams. FIG. 2 is a block diagram showing thestructure of an ultrasonic imaging apparatus. In FIG. 2, 1 is atransmission pulse circuit for generating pulse signals for drivingultrasonic transducers to transmit ultrasound. 2 is a transmission delaycircuit for providing each ultrasonic transducer driven by therespective pulse signals output from the transmission pulse circuit 1with the determined delay time corresponding to each driven transducer.3 is a transmitting/receiving separation circuit for passing signalsfrom the transmission pulse circuit to the ultrasonic transducer whentransmitting ultrasonic waves, and from the ultrasonic transducer sideto the receiving circuit side when receiving ultrasonic waves. 4 is atransducer selecting switch circuit for selecting from among theultrasonic transducers that are arrayed on the ultrasonic probe atransducer group (an aperture) to transmit and receive. 5 is aultrasonic probe having said array of ultrasonic transducers. 6 is areception circuit for amplifying extremely weak echo signals, which areultrasonic waves reflected from an object, which then have beenconverted into an electric signal by the transducer. 7 is an A/Dconverter (ADC) for converting analog echo signals into a digitalsignal, said analog echoes being output from the receiving circuit 6. 8is a digital delay unit for delaying a digital echo signal that isoutput from the ADC 7. 9 is an adder circuit for forming an ultrasonicreceiving beam signal by adding echo signals that are output from thedelay unit 8. 10 is a signal processing unit for preprocessing saidsignals that are output from the adder circuit for conversion to images,that is, performing logarithmic compression, filtering and γ correctionon this input signal. 11 is a display unit for successively storing thesignals that are output from the signal processing unit 10 together withthe position of the respective ultrasonic beam, as well as convertingultrasonic scanning into display scanning to output it, and displayingthe image on a displaying device. 12 is a sampling signal generatingunit for generating sampling signals at the ADC 7. 13 is a delaycontrolling unit for providing delay data to the transmission delaycircuit 2 and the digital delay unit 8. 14 is a central processing unit(CPU) for collectively controlling said constituent features.

[0039] Next, the operation of the ultrasonic imaging apparatus that hasthe structure shown in FIG. 2 will be described. First, an operatorperforms initial setting of the apparatus before beginning examination.At the initial setting, the operator identifies the part of the objectto be examined, estimates the depth of said part to be examined from thebody surface, and sets focusing depth of the transmitting wave. In theapparatus, transmission delay data (Dt) is calculated for this setfocusing depth from the determined average value of ultrasonicpropagation velocity of the organism by the CPU 14, and then said Dt isprovided to the transmission delay circuit 2 through the delay controlunit 13 when transmitting. Besides, in order to enable the operator toinput sonic velocity manually to the apparatus, sonic velocity inputtingdevice can be furnished in the console and the initial setting can bemade with this inputted value of sonic velocity.

[0040] At least, after performing said initial setting, the operatorapplies the ultrasonic probe 5 to the surface of the examined part andinputs a command to begin ultrasonic scanning through the console. Then,the aperture of the prove to be used is selected and the transmissiondelay data (Dt) is set, and as well the reception delay data (Dr) ofdigital delay unit 8 at time of reception is set according to saidaverage sonic velocity, and then the scanning begins. When the scanningbegins, the driving pulse is output from the transmission circuit 1, andthe delay time calculated for each ultrasonic transducer in the aboveaperture is applied to the driving pulse to be sent to that transducerby the transmission delay circuit 2. Then, the driving pulse is input tothe transducer selecting switch circuit (a multiplexer circuit) 4through the transmitting/receiving separation circuit 3. At thetransducer selecting switch circuit 4, connection switchover isperformed such that each inputted driving pulse is output to itsassigned transducer with the delay time applied to that pulse. The probeis driven with the driving pulse that is output from the transducerselecting switch circuit 4.

[0041] The selected transducer group of the probe is driven in order ofshortness of delay time of transmission of ultrasound. The ultrasoundtransmitted from the driven transducer group into the living bodypropagates within the living body such that every ultrasonic wavesurface simultaneously arrives with the same phase at the transmissionfocus point that is set at the initial setting. Then, when a tissuehaving different acoustic impedance exists in the propagating course ofthe ultrasound, a part of ultrasound is reflected at the boundarysurface of the tissue and the reflected wave (echo) returns towards theprobe. The echoes return to the probe in turn according to thepropagation of ultrasound that is transmitted from the shallow part tothe deep part of the living body.

[0042] Said echoes are received by the transducers driven fortransmitting, or by a transducer group of an aperture switched fromsmaller to larger aperture with the passage of time, and then it istransformed into an electric signal (echo signals). The amplifyingprocess is separately performed at each transducer element line(channel) in the receiving circuit 6 to the echo signals that becomeelectric signals at the transducer, through the transducer selectingswitch circuit 4 and the transmitting/receiving separation circuit 3,and then, the amplified signals are inputted to the ADC 9 at the eachchannel. The ADC 9 converts the echo signals of each channel intodigital signals according to the timing of the sampling signalsgenerated by the sampling signal generating means 12. Then, thedigitalized echo signals are input to the digital delay unit 8.

[0043] The digital delay unit 8 is composed of digital delay circuitsfor each channel. It performs delay control on inputted echo signals byusing said reception delay data that is provided from the delay controlunit 13 controlled by the CPU 14, and the echo signals reflected from acertain point in the object (a point along the beam which is received)are outputted to the adder circuit 9 after adjusting the time phase ofeach channel so that these echo signals are all output at the same time.

[0044] The adder circuit 9 adds the echo signals of each channel, whichhave been outputted from the digital delay unit, forms ultrasonicreceived beam signals, and outputs them. As a result of said digitaldelay control and addition, there are formed echo beams that arereceived by the dynamic focus method well known in this field of theinvention. Then, preprocessing such as logarithmic compression,filtering process, or γ correction are performed to the received beamsignals, and then the signals are outputted to the display unit 12. Thedisplay unit 12 stores inputted beam signals in the memory for a time.

[0045] Transmission and reception of said ultrasound and its signalprocessing are repeated with each selection switchover of the ultrasonictransducer or direction change of ultrasonic beam. The received signalsare taken into the display unit in turn, and beam signals inputted byeach cycle of said transmission and reception form an image.

[0046] And, said stored contents in the memory that have become an imageare read out while synchronizing with the scanning of the CRT display.In this manner, the inside of the living body is imaged and displayed.

[0047] By using the data obtained by said transmission and reception ofultrasound, the delay control unit 13 calculates the delay data forfocusing at the next ultrasonic scanning. The structure and theoperation of said delay control unit 13 will be described below.

[0048]FIG. 1 is a block diagram showing the detailed structure of thedelay control unit 13 connected to the digital delay unit 8 of theultrasonic imaging apparatus shown in FIG. 2. In FIG. 1, 82 is a digitaldelay data generating unit for providing delay data to the digital delayunit 8, and 131 is a delay time error calculating unit to calculate thedelay error from a plurality of outputted echo signals, on which delaycontrol has been performed by the digital delay unit 8.

[0049] Delay accuracy is improved and a good image can be obtained byadopting the above structure when the calculation result of the delaytime error calculating unit 131 is fed back to the digital delay datagenerating unit 82 to perform delay control for the next ultrasonictransmission and reception. But as for calculation in the delay timeerror-calculating unit 131, if unexpected signal data is mixed with thedata obtained with a tentative scanning, it becomes difficult tocalculate accurate correction value. Therefore, an output of the delaytime error calculating unit 131 must be regarded merely as a provisionalstandard.

[0050] Accordingly, an ultrasonic imaging apparatus of the embodiment ofthe present invention further comprises a sound velocity-derived delaytime storing unit 132 that is composed of, for example, ROM for storingin advance a group of delay times corresponding to the sonic velocitiesof various mediums, the delay time comparing unit 133 for comparing thestored value of delay time error data obtained in the delay time errorcalculating unit 131 with stored values of the sonic velocity-deriveddelay time storing unit 132, and outputting the delay time datacorresponding to the sonic velocity closest to that of the object, thesonic velocity data storing unit 134 for storing which sonic velocityresults in which delay time group stored in the sonic velocity-deriveddelay time storing unit 132, and the sonic velocity/medium selectingunit 135 for selecting sonic velocity based on delay time data, storedin the delay time storing unit, that had been output by the delay timecomparing unit 133.

[0051] As is shown in FIG. 2, the delay time error calculating unitcomprises delay time error detecting circuits 131 a of (M−1) in numberfor detecting delay time errors by inputting the output of the digitaldelay circuits of two adjoining channels 8-l to 8-M, and the delay timeerror distribution data forming circuit 131 b for expressing output dataof this delay time error detecting circuit as distribution data.

[0052] Here, for the sonic velocity-derived delay time storing unit 132,it is preferable to calculate in advance the delay time error data inthe case of changing the sonic velocity by predetermined sonic velocityincrements or decrements from a certain standard sonic velocitydetermined, for example, from the delay time error at each channel forsaid average sonic velocity, and store the data as a table. Then, storeddata of this time is made into a graph in order to be visuallyunderstood is shown in FIG. 3. In FIG. 3, the horizontal axis indicatesthe number of the channel and the vertical axis indicates delay timeerror, and the plurality of lines in the graph indicates the relationbetween the channels and the delay time error, for a plurality ofrespective sonic velocities as the parameter. The number of channels ofultrasonic transducers carrying out transmission and reception is M.Incidentally, FIG. 3 is an example of linear scanning. In FIG. 3, sonicvelocity Vo is chosen to be that velocity in which the delay time erroris the constant value of zero at each channel. This is the reason thatthe present invention adopts the method of performing a tentativescanning by using the standard sonic velocity Vo, and calculating delaytime errors that occur. Referring to FIG. 3, when the sonic velocity isfaster than the standard sonic velocity Vo, the delay time error line isconvex downward with the lowest point at the center of the group oftransducers (M/2). And, when sonic velocity is slower than the standardsonic velocity, the delay time error line is convex upward with thehighest point at the center of the group of transducers (M/2). Datastored in the sonic velocity-derived delay time storing unit 132 in thismanner, as data for the standard sonic velocity and for velocitiesdeviating from this, contributes to lowering the storage capacity neededin the memory unit.

[0053] Thus, by adding the sonic velocity-derived delay time storingunit 132, the delay time comparing unit 133, the sonic velocity storingunit 134 and the sonic velocity/medium selecting unit 135, an ultrasonicimaging apparatus of the embodiment of the present invention enables notonly delay time correction for an adaptive imaging method which isgenerally called, but also estimation of sonic velocity of theultrasonic propagating medium.

[0054] Hereinafter, the principle and the operation of the part of anultrasonic imaging apparatus containing an embodiment of the presentinvention concerning the present invention will be described. First, theultrasonic propagation velocity of the medium is provisionally set to bethe average sonic velocity of a living body in the digital delay unit 8and the transmission delay data based on this average sonic velocity isset in the transmission delay circuit 2, and then ultrasonic scanning ofsaid tentative scanning is performed. The reception delay data (Dr)corresponding to said average sonic velocity is supplied from thedigital delay control unit 82 to the digital delay unit 8 so as toreceive the echo signals which will be formed into a received beam bythe digital delay unit 8, and then the echo signals are input to eachchannel of the delay time error calculating unit 131. The delay errorcalculating unit 131 calculates delay time error (Dn) for each channelafter the echo signals of adjoining channels such as 1CH and 2CH, 2CHand 3CH, . . . , (M−1)CH and MCH are input in the delay time detectingcircuit, using for example the correlation method disclosed in saidJapanese Patent Laid-open Publication No. Heisei 4-252576, and thencalculates a delay time error data group consisting of D1, D2, . . . ,Dm as a distribution data. The purpose of calculating the delay timeerror data as a distribution is to prevent errors due to said unexpectednoise or the like. Incidentally, calculation of the delay time error bythe delay error calculating unit 131 can be done for the received beamin all scanning region in case of scanning in the living body whilechanging the position or the direction of a ultrasonic beam by a probe.It can be also done by setting a region of interest where an organ to beexamined exists, and calculating the delay time error of the receivedbeam only in said region.

[0055] Next, ultrasonic propagation velocity in the living body iscalculated from said distribution of delay time error. In the sonicvelocity-derived delay time storing unit 132, delay time datacorresponding to plausible sonic velocities is stored in a form makingsonic velocity a parameter. Stored contents of said sonicvelocity-derived delay time storing unit 132 are also stored as delaytime distribution data for each channel in the cases of various sonicvelocities. Then, stored contents of the delay error storing unit 131and the sonic velocity-derived delay time calculating unit 132 areinputted to the delay time comparing unit 133 to be compared, and thedelay time distribution in the sonic velocity-derived delay time storingunit 132 which is closest to the distribution of output data from thedelay error calculating unit 131 is selected. At this time, the delaytime distributions in the sonic velocity-derived delay time storing unit132, which are the subject with which comparison is made, is stored asdelay time distributions for discrete sonic velocity values. Then, ifthe assumed sonic velocity values are few in number so that there arelarge gaps, the distribution of output data from the delay errorcalculating unit 131 does not often match well with the delay timedistribution stored in the sonic velocity-derived delay time storingunit 132, and the most closely matching value might be the mean betweentwo of them.

[0056] Assuming such a case, it is preferable to add a calculationcircuit for selecting two values close to the output from the delayerror calculating unit 131 within the delay time error data stored inthe sonic velocity-derived delay time storing unit 132, and forperforming correction calculation based on an interpolation method or anextrapolation method by using said two values at the latter part of thecomparing unit in the delay time comparing unit 133, and use thiscalculation result for determining sonic velocity. Incidentally, suchcorrection calculation is not necessary when sonic velocity of themedium is estimated to a sufficient degree of accuracy, and this isstored in the sonic velocity-derived delay time storing unit 132. To beable to perform the comparison in the delay time comparing unit 133simply, it is useful to use a method utilizing the fact that the delaytime distribution to the input of a plurality of ultrasound signals canbe approximated as a quadratic concave surface to reduce the informationto be dealt with. Moreover, calculating the delay time distribution atdiscrete interval and applying a linear line to the array of delay timediscrete value is useful because the information to be dealt with isfurther reduced.

[0057] Next, the stored delay time data for the delay time valuesmatching the output from delay error calculating unit 131 is inputted tothe sonic velocity/medium selecting unit 134 and the sonic velocity iscalculated referring to the delay time distribution in the sonicvelocity storing unit 135.

[0058] To improve accuracy of the sonic velocity thus calculated, thereceived ultrasonic signal must have enough intensity. But in thestructure of an apparatus dealing with fundamental waves with the samefrequency as the transmitting frequency and harmonic waves generatedfrom an ultrasonic medium, intensity of the harmonic wave is generallyweaker than that of the fundamental wave. Thus, it is useful foraccurate sonic velocity estimation to make the signal amplificationfactor of the harmonic wave larger than that of the fundamental wave tocompensate for the signal reduction. Similarly, if it is known that thereduction degree of ultrasonic medium is different depending ontransmitting frequency and path length, it is effective to amplify thesignal by using a correction value that can be calculated in advance.

[0059] The sound velocity data selected by the sonic velocity selectingunit 134 is fed back to the CPU 14 to form the delay data in the digitaldelay unit 8 for the ultrasonic scanning of the next examination. Also,the sonic velocity data is provided to the display unit 12 through theCPU 14 as a numerical value on the image of the display unit 12, asshown in FIG. 5, where in the area labeled with the number 2 the sonicvelocity is shown as V=1,500.

[0060] In calculating the delay error at the delay error calculatingunit 131, a plurality of delay time error data can be obtained by usingthe data obtained by scanning the broad region extending both in thedepth direction and in the lateral direction. In this method, obtainedsound velocities are outputted as different values in a plurality ofregions. It is possible to use all these data for scanning in anexamination. But there are many cases that it is more useful to use onlyone sonic velocity representative of the whole region or of the regionof interest (ROI). For example, calculating a typical sonic velocity inthe whole region and using correction data based on it, an image ofaverage sharpness over the whole region can be obtained. Alternatively,by calculating the sonic velocity only of the ROI and using thecorrection data based on this only an image in which only the ROI issharply focused can be obtained. It is possible to use one of thesemethods selectively or two of them jointly, according to the purpose.

[0061] To calculate the sonic velocity that is typical in the wholeregion, it is useful to add a circuit structure for estimating andselecting from among the sub-regions in this region the sub-region thatsends back the most reliable values to the medium/sonic velocityselecting unit 134. For example, if the delay time error distributionoutputted from the delay time error calculating unit 131 is tilted, itwould appear that the beam would pass through this object in a directiondifferent from the original beam direction, because the beam is made toperform focusing on an object having high level echo. It is difficult todetermine the sonic velocity of a region sending back such delay timeerror values. It also is more difficult to determine sonic velocity asthe absolute difference d between the delay time error distributionstored in the sonic velocity-derived delay time storing unit 132 anddelay time D′ corresponding to said medium becomes larger. Thus it ispreferable to select only a region where the intensity A of the receivedsignal is large for calculating the typical sonic velocity.

[0062] In other words, an estimated coefficient K for selecting onetypical sonic velocity out of sound velocities calculated in a pluralityof regions is preferably calculated with the formula K=A/α+β/d+γ/θ andthen the sonic velocity in the region where K is maximum is selected.Here, α, β, γ are values freely chosen for performing suitable weightingto each estimated item.

[0063] Also, when calculating the sonic velocity in a specific region,if there is an element moving in the ROI (for example, bodily movementdue to heartbeat in a human body) it is effective to continuouslytransmit ultrasound a number of times to one part and estimate the sonicvelocity by averaging the delay error information of each receivedsignal because the sonic velocity is not so affected by the bodilymovement and is stable. Further, as for the elements like cardiac valvesthat move especially fast, it is possible to calculate the sonicvelocity accurately by obtaining the delay error informationsynchronized with the electrocardiogram in addition to the above. And,when the ROI is changed from moving organs to other non-moving organs,it is efficient to switch from the mode of repeated ultrasoundtransmission at one place to the mode of transmission only one time.

[0064] As said delay error measuring calculation methods, there are:

[0065] a method of detecting phase difference between adjoining channelsby correlation processing;

[0066] a method of performing complex multiplication of signals ofadjoining channels which have been phased with the main receivedfrequency to isolate the frequency difference component, and thencalculating tan θ by dividing its real part by the imaginary part tocalculate the phase difference; and

[0067] a method of varying the delay time of each channel so that theyconverge in order to set the noticed region in displayed to have themaximum histogram height and signal intensity.

[0068] Since the delay error calculating unit 131 of the aboveembodiment is known in said reference, detailed explanation is hereomitted. Any of the known methods above can be applied.

[0069] The present invention can be modified in various ways. Forexample, in said embodiment, the sound velocity is calculated and delaydata is modified for imaging. But, because the output from the delayerror detecting circuit in the latter part of the digital delay unitincludes the delay error information, it can be input withoutmodification as the delay error of each channel in the CPU 14, where itis transformed into delay data, input to the delay data unit 82 forimaging, corrected with the average sonic velocity of the whole imagingregion to improve the image, and then perform sonic velocity correctiononly for the ROI according to said embodiment. By this process, theimage quality of the whole image can be improved, and the image of theROI becomes still clearer.

[0070] Also, as a method of displaying calculated sonic velocity, theexample of displaying the sonic velocity as a numerical value in saidembodiment has been explained. However, by scanning ultrasonic beam bothin the depth direction and in the lateral direction, the sonic velocitycan be calculated in a plurality of regions. If the distribution of allthese calculated sonic velocities is made visible in the display, it ispossible to observe that the organ is in the process of pathologicalchange even when there is no change of the shape in the living body yet.Various embodiments for displaying it can be considered, display as asonic velocity map may be the useful method.

[0071] Some examples of displaying methods of the sonic velocity map areas follows:

[0072] a method of making a sonic velocity map image such as the oneshown in FIG. 5(b) and displaying this and an ultrasonic image (crosssectional image) shown in FIG. 5(a) side by side;

[0073] a method of selecting either the ultrasonic image or the sonicvelocity map image for display on a screen of the displaying device;

[0074] a method of displaying the ultrasonic image and the sonicvelocity map image overlapped,

[0075] a method of displaying the ultrasonic image by applying to thebrightness value of each point on the image a brightness modulationcorresponding to the sonic velocity of that point;

[0076] a method of displaying the monochromatic ultrasonic image afteradding to each pixel a color modulation corresponding to that pixel ofthe sonic velocity map image;

[0077] a method of displaying the ultrasonic image superposed on thesonic velocity map where the sonic velocity values are offset from thecorrespondent pixel of the ultrasonic image.

[0078] It is possible to use one of these or a combination depending onthe purpose. Of course, it is also useful to display a plurality of thesonic velocities as numerals or to display a typical sonic velocityvalue selected out of a plurality of sonic velocities by one of theabove methods. Incidentally, when displaying the sonic velocity mapimage, it is helpful to display a scale (300 in FIG. 5) that indicatescontrast or color of map image near the map image to help a doctor readit.

[0079] Also, when the present invention not only to a B-modemonochromatic image used in an ultrasonic image diagnostic apparatus butalso a colored image (a color flow mapping image) is applied, it ispossible to accurately display the positional relation of themonochromatic image and the colored image. When applied to themonochromatic image and the Doppler image, it is possible to improveaccuracy of the positioning of Doppler signal reception region. Further,when applied to an M-mode image, it is possible to improve the distanceaccuracy. In another method, the degree of improvement of image qualitycan be indicated by first displaying the image with weak contrast andthen displaying the part of the image whose image quality has beenimproved by lightly displaying it with usual contrast. And whenconstructing a phase adjustment circuit such that has two lines orshifts among a plurality of lines by time-sharing, the degree ofimprovement of image quality can be compared because images provided bythe usual focus and provided by modified focus can be simultaneouslyobtained.

[0080] And furthermore, complicatedly alternating transmission waveforms are used in the coded transmission and reception, a technique tomeasure good reflection signals which does not increase the momentarytransmission energy but increases the total energy. Thus, it can beinferred that the conventional delay error estimation method describedabove might easily make a wrong estimate. In this case, after performingusual transmission and reception and improving focusing accuracy byperforming said sonic velocity estimation, then, the coded transmissionand reception are performed. By this process, the accuracy of the delaytime error estimation method can be improved similarly to the usualtransmission and reception.

[0081] In this embodiment, the case of obtaining two-dimensionalsectional images with a one-dimensional array of transducers isdescribed. But also, the same process can be done and the same effectcan be obtained in measuring and displaying a two-dimensional or athree-dimensional image by using a ring array or a two-dimensional arrayof transducers.

[0082] As described above, according to the present invention the sonicvelocity of the medium can be quickly calculated with a simplecalculation without making any assumption about the medium, andultrasonic imaging can be performed by using the delay time data basedon this sonic velocity. Also, the apparatus can automatically calculatesuitable sonic velocity without an operator inputting the sonic velocityof the medium. Thus, the operationality of the apparatus is improved.

[0083] Furthermore, according to the present invention, a uniform andclearer image can be obtained throughout the whole region of ultrasonicscanning

[0084] Furthermore, because the apparatus displays the calculated sonicvelocity data automatically, the operator can find not only sonicvelocity, but also distribution of sonic velocity in the living body.

1. An ultrasonic imaging apparatus comprising: an ultrasonic probehaving a plurality of built-in transducers for transmitting ultrasonicwaves towards an object to be examined and receiving the echoes from it;means for converting each echo signal that is output from the pluralityof transducers in said ultrasonic probe into digital signals; phaseadjustment means for adjusting phase of echo signals by applyingpredetermined delay time data to each digitized echo signal that isoutput from said digital signal converting means; means for calculatingdelay time data corresponding to ultrasonic propagation velocity in theobject, using the output signals from said phase adjusting means; meansfor forming received beam signals by applying the delay time datacalculated by said delay time data calculating means to the outputsignal of said phase adjustment means; and means for displaying an imageon a displaying means by image-processing the received beam signalsformed by said received beam signal forming means.
 2. An ultrasonicimaging apparatus according to claim 1, wherein said delay time datacalculating means comprises: means for calculating delay time errorsfrom echo signals of a plurality of transducers which are contributed tothe signals output from said phase adjustment means; storing means forstoring delay time error data corresponding to a plurality of ultrasonicpropagation velocities; and a sonic velocity selecting unit forselecting the ultrasonic propagation velocity by comparing the output ofsaid calculating means with delay time data stored in said storingmeans.
 3. An ultrasonic apparatus according to claim 2, wherein delaytime errors corresponding to a plurality of ultrasonic transducerchannels are stored as a plurality of delay time distributions usingsonic velocity as a parameter, in said delay time error data storingmeans.
 4. An ultrasonic imaging apparatus according to claim 2, whereinsaid delay time error data calculating means calculates delay time errorby using a certain portion of output signals of said phase adjustmentmeans in the depth direction.
 5. An ultrasonic imaging apparatusaccording to claim 2 wherein said delay time error calculating meanscalculates delay time errors by using output data of said phaseadjustment means in all region in the depth direction, as well as thatthis calculation is performed throughout a predetermined ultrasonicscanning region that is formed by a plurality of received beams.
 6. Anultrasonic imaging apparatus according to claim 1, wherein sonicvelocity storing means is provided for storing ultrasonic propagationvelocity corresponding to a plurality of delay time distributions thatare stored in said delay data storing means, and said sonic velocityselecting unit calculates sonic velocity corresponding to the selecteddelay time data by comparing with the contents stored in said sonicvelocity data storing means.
 7. An ultrasonic imaging apparatusaccording to claim 6, said apparatus comprises means for displaying thesonic velocity data being calculated at said sonic velocity selectingunit on the screen of said displaying means.
 8. An ultrasonic imagingapparatus according to claim 1, said apparatus comprises means forsetting ultrasound propagation velocity estimated from the physicalconstitution of the object to be examined, and means for calculatingerrors in this propagation velocity using the ultrasonic propagationvelocity being set at said setting means and ultrasonic propagationvelocity in the object that is calculated by using the output signal ofsaid phase adjustment means, wherein said received beam signal formingmeans produces received beam signals by applying propagation velocityerrors calculated by said calculating means and ultrasonic propagationvelocity being set at said setting means to output signals of said phaseadjustment means.
 9. An ultrasonic imaging apparatus according to claim8, said apparatus comprises means for transforming delay time errorscalculated by using data of a plurality of output signals of said phaseadjusting means on all region in the depth direction into sonic velocitydata distribution, and then displaying it as a sonic velocitydistribution image on the screen of said display means.
 10. Anultrasonic imaging apparatus according to claim 8, wherein the sonicvelocity distribution image is displayed with hues varied in accordancewith difference of the sound velocity.
 11. An ultrasonic imagingapparatus according to claim 8, wherein the sonic velocity distributionimage and the ultrasonic cross sectional image are displayedsimultaneously on the display screen of said display means.
 12. Anultrasonic imaging apparatus according to claim 11, wherein the sonicvelocity distribution image is displayed by superimposing the ultrasoniccross sectional image on it.